Implement distributed synchronization features

- Added a sync manager to handle distributed synchronization across relay peers, initialized in the main application run function.
- Enhanced the event handling to update the serial number for synchronization when events are processed.
- Introduced new API endpoints for synchronization, allowing peers to fetch the current serial number and events within a specified range.
- Implemented peer request validation for synchronization endpoints to ensure authorized access based on NIP-98 authentication.
- Updated configuration to support relay peers for synchronization.
- Bumped version to v0.24.0 to reflect these changes.

app/handle-event.go

@@ -455,6 +455,12 @@ func (l *Listener) HandleEvent(msg []byte) (err error) {
 		chk.E(err)
 		return
 	}
+
+	// Update serial for distributed synchronization
+	if l.syncManager != nil {
+		l.syncManager.UpdateSerial()
+		log.D.F("updated serial for event %s", hex.Enc(env.E.ID))
+	}
 	// Send a success response storing
 	if err = Ok.Ok(l, env, ""); chk.E(err) {
 		return